Communicate whether passive event listeners exist to cc.

third_party/WebKit/public/platform/WebEventListenerProperties.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef WebEventListenerProperties_h
+#define WebEventListenerProperties_h
+
+#include "WebCommon.h"
+
+namespace blink {
+
+enum class WebEventListenerClass {

[Rick Byers, 2016/02/02 21:44:46]

mention here that "touch" includes pointer event listeners too.
And I guess "MouseWheel" means DOM "wheel" and "mousewheel" events.

[dtapuska, 2016/02/03 16:30:58]

Done.

+    Touch,
+    MouseWheel
+};
+
+enum class WebEventListenerProperties {

[Rick Byers, 2016/02/02 21:44:46]

Please add a brief comment (in particular I find the word "properties" a little
non-obvious, but not worth renaming everything <grin>).  Maybe "Indicates the
variety of event listeners present for a given class of event"?

[dtapuska, 2016/02/03 16:30:58]

Done.

+    Nothing = 0x0, // This should be "None"; but None #defined in X11's X.h
+    Blocking = 0x1,
+    Passive = 0x2,

[Rick Byers, 2016/02/02 21:44:46]

Do you really need to differentiate the 'Blocking|Passive' and 'Blocking' cases?
 If not, I think this would be simpler as a 3 element enum (can just do equality
or even < > comparison instead of bits).  Also folding in this 4th case may help
reduce the risk of certain types of bugs (we don't want the presense/absense of
passive listeners to be observable).

[dtapuska, 2016/02/03 16:30:58]

Done.

+};
+inline WebEventListenerProperties operator| (WebEventListenerProperties a, WebEventListenerProperties b) { return static_cast<WebEventListenerProperties>(static_cast<int32_t>(a) | static_cast<int32_t>(b)); }
+inline WebEventListenerProperties& operator|= (WebEventListenerProperties& a, WebEventListenerProperties b) { return a = a | b; }
+inline WebEventListenerProperties operator&(WebEventListenerProperties a, WebEventListenerProperties b) { return static_cast<WebEventListenerProperties>(static_cast<int32_t>(a) & static_cast<int32_t>(b)); }
+inline WebEventListenerProperties& operator&= (WebEventListenerProperties& a, WebEventListenerProperties b) { return a = a & b; }
+
+} // namespace blink
+
+#endif